Return to ctxsw.s CVS log

Up to [XINU] / xinu / sys

Annotation of xinu/sys/ctxsw.s, revision 1.1.1.2

1.1.1.2 ! root        1: |* ctxsw.s - ctxsw
1.1       root        2: 
1.1.1.2 ! root        3: |*-----------------------------------------------------------------------------
        !             4: |* ctxsw  --   actually perform context switch, saving and loading registers
        !             5: |*             This routine is executed in kernel mode.
        !             6: |*
        !             7: |*             Upon entry, d0-d7, a0-a6, the ssp, the sr, and the pc are
        !             8: |*             saved.  The usp is ignored.
        !             9: |*
        !            10: |*             Upon exit, all registers saved are restored, and the value
        !            11: |*             of the supervisor stack pointer is copied into the user 
        !            12: |*             stack pointer.
        !            13: |*-----------------------------------------------------------------------------
1.1       root       14: 
1.1.1.2 ! root       15:        .data
1.1       root       16:        .text
1.1.1.2 ! root       17:        .globl  _ctxsw
        !            18: _ctxsw:
        !            19:        movl    a0,     sp@-            | Save A0 onto old stack        
        !            20:        movl    sp@(8), a0              | Move address of old area into A0 
        !            21:        moveml  #0xffff,a0@             | Save all registers            
        !            22:        movl    sp@,    a0@(32)         | Put original A0 in old savearea       
        !            23:        addql   #8,     a0@(60)         | Move SP beyond return address
        !            24:                                        |       as if a return has occured
        !            25:        addl    #64,    a0              | Skip past registers d0-7,a0-7
        !            26:        movw    #0,     a0@+            | Pad SR savearea, since SR is a word
        !            27:        movw    sr,     a0@+            | Save SR in old savearea       
        !            28:        movl    sp@(4), a0@+            | Save PC in old savearea       
        !            29: 
        !            30: |Save image:d0,d1,d2,d3,d4,d5,d6,d7,a0,a1,a2,a3,a4,a5,a6,ssp,0x00, sr, pc
        !            31: |            0  4  8 12 16 20 24 28 32 36 40 44 48 52 56  60  64   66  68 
        !            32: 
        !            33:        movl    sp@(12),a0              | Move address of new area into A0
        !            34:        moveml  a0@,#0x7fff             | Restore all regs (even A0) except SP
        !            35:        movl    sp@(12),a0              | Move address of new area into A0 again
        !            36:        movl    a0@(60),sp              | Put  SSP into both kernel stack
        !            37:        movl    sp,     usp             |      and            user  stack
        !            38:        movl    a0@(68),sp@-            | Move PC onto current stack    
        !            39:        movw    a0@(66),sp@-            | Move SR onto current stack
        !            40:        movl    a0@(32),a0              | Restore A0 from new area      
        !            41: |      rte
        !            42:        movw    sp@+,sr                 | (rte works differently on 68010)
        !            43:        rts                             | so do 68000-rte in effect this way
        !            44:        .data

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.